1. Field of the Invention
The present invention relates generally to the field of enclosures housing electrical equipment. More particularly, the invention relates to a technique for positively identifying that electrical power is not present in at least a portion of an enclosure housing an electrical device.
2. Description of the Related Art
Many types of electrical devices are comprised of electrical components housed within an enclosure. These enclosures may serve many purposes. For example, an enclosure may be used to protect the electrical components of the device from the environment. Alternatively, an enclosure may be used to protect people from the electrical components housed within the enclosure and, more importantly, from the electrical hazards associated therewith.
Occasionally, it may be desirable to enter an enclosure to access the electrical components. For safety reasons, it is preferable that there be no hazardous power be supplied to an electrical device when entering the enclosure to access the electrical components. The components must be considered energized until the absence of any hazardous voltages within the enclosure is verified.
The presence or absence of a hazardous voltage within an electrical device may be detected with a voltmeter. However, typically the enclosure must be opened to enable a user to access the electrical components with the voltmeter. However, because each components has not been verified as “de-energized”, the device must still be considered energized, and special safety precautions may be required. The special safety precautions often require personal protective equipment to be used, which may be awkward to work in and hamper the taking of measurements. In addition, taking voltage measurements with a voltmeter may not detect when there is a temporary loss of power upstream of the device. This may produce a false indication that power to the electrical device has been removed. When the power upstream of the device is restored, the electrical components within the enclosure may be re-energized. Therefore, this method does provide a positive verification that the electrical device has been de-energized and, most importantly, exposes the user to electrical hazards.
A light may be connected at a point within an electrical circuit of the device to indicate the presence of a voltage. The light may be connected in the electrical circuit so that it is illuminated if there is a voltage present, thereby providing an indication of the presence of a voltage in the circuit. However, the converse is not true. For example, if the light is not illuminated, it may mean that there is no voltage in the circuit. However, it may also mean that the bulb simply has failed. In addition, this method also cannot detect a temporary loss of power upstream of the device. Therefore, this method also does provide a positive verification of the absence of a voltage within the device.
In addition, it may be desired to detect voltages within an electrical device to troubleshoot a problem within the electrical device or simply to verify the proper operation of the electrical components within the device. For example, if a voltage is detected at a point upstream of a component, but not detected at a point downstream of the component, then there is an open in the circuit between the two points. The open in the circuit may be due to the failure of the component.
A need exists for a technique to enable the absence of a hazardous voltage within an electrical device to be verified without a person having to access the interior of the device to take voltage measurements. Furthermore, there is a need for a technique to enable a positive indication that a voltage is not present within an electrical device to be provided to a person before entering the electrical device.